Cédric Bastien Jurek Czyzowicz Wojciech Fraczak Wojciech Rytter Equivalence of Functions Represented by Simple Context-Free Grammars with Output. 71-82 2006 conf/dlt/2006 Developments in Language Theory http://dx.doi.org/10.1007/11779148_8 db/conf/dlt/dlt2006.html#BastienCFR06